Igniter plug



United States Patent O IGNITER PLUG Earl W. Pierce and Harley E. Fortier, Flint, Mich., as-

swors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Dec. 20, 1957, Ser. No. 704,167

Claims. (Cl. 313-131) gas turbine engines. Another object of the invention is to provide an igniter plug of the low tension type which is adapted to project an intense, large spark and which has a long useful life. Another object is the provision of an improved igniter plug of the type described having improved means for sealing the centerwire wit-hin the insulator assembly.

These and other objects and advantages of the invention will appear more clearly from the following description of a preferred embodiment and from the drawings in which:

Figure l is a side view in partial section of the preferred embodiment ofthe invention;

Figure 2 is a bottom viewV of the igniter plug shown in Figure 1';

Figure 3 is an enlarged view in section of the centerwire seal portion of the igniter plug shown in Figure 1; and

Figure 4 is an enlarged view in section of the tiring end of the ignite-r plug shown in Figure l.

Referring now to the drawings, the igniter plug includes a metal shell 6 which is constructed in three sections suitably joined together as by the brazed joint shown at S and by the threaded joint shown at 10. Cooperating fianges as shown at 1-1- assure that the lower section of the shell will not become disassembled in the event the brazed joint should fail. A suitable mounting pad i2 is brazed to the shell so that the igniter plug can be secured to the combustion chamber wall of a gas turbine engine. The lower end of the tubular metal shell 6 is formed with al thickened portion 14 to provide a reduced intern diameter and terminates with an inwardly extending annular flange 16 which serves as the ground electrode for the igniter. Y

Secured within the lower end of the shell is a lower, generally tubular-shapedv `alumina-base ceramic insulator 13 having a lower end of enlarged internal diameter to form a recess 19, and also of enlarged external diameter to t snugly within the lower portion 14 of the shell. This insulator is secured within the shell by means of ametalv nut 28 which threadedly engages the shell, the insuiator thereby being pressed between said nut and the ilange i6 at the lower end of the shell which serves as the ground electrode of the igniter. An upper through-bored alumina-base insulator 22 is secured within the upper end of the shell by means of conventional shoulder 24, this upper insulator having a lower end portion 2o tting concentrically into upper enlarged endZS of the lower insulator.

Extending through the aligned bores of insulators 18 and 2.2 is a metal centerwire 38 having an upper end 32 which extends above the insulators and serves as the 2,939,983 Patented June 7, 196@ ICC connecting terminal for the igniter. The centerwire is hermetically sealed to the' upper insulator by means of a metal sleeve 34, the upper end of which ts snugly around and is brazed to the center wire as shown at 36 and the lower end of which has an enlarged internal diameter such that it is of reduced wall thickness and thereby spaced from the centerwire. The bottom of the sleeve 34 is positioned in a counterbore 38- in the upper insulator and a sealed joint between the sleeve and the insulator is formed by a mass of fused glass 39 having substantially the same coeihcient oi' expansion as that of the sleeve. Where the sleeve is made of Kovar (typical analysis: iron 54%, nickel 28%, cobalt 18%) the glass 39 may consist of 2% B203 and 98% alkali borosilicate glass (typical analysis: SiOg; 64.8%, A1203 16.2%, B203 16.5%, Nag() 3.4%, K2() 3%, Mg() 3%, CaO 3%). The important advantage of this seal structure is its high resistance to cracking or other failure from rapid temperature changes.

The centerwireV 3G is formed with a. cylindrical head portion 4? adjacent its lower end which is positioned within recess 19 formed at the end of insulator 18. The centerwire' terminates with a projection 42 extending below Vhead portion 4Q, this projection tting snugly into and extending partially through a flat-sided ring 44 of insulator or semi-conductor material. The centerwire projection 42 serves as the center electrode of the igniter, its base surface being spaced from and cooperating with flange 1G of the shell to form the spark gap. The ring 44 may be made of any suitable material which will electrically insulate the centerwire from the ground electrode. Preferably itshould be a semieconductor such, for example, as silicon carbide, or of an insulator material provided with a semi-conductive coating such `as copper oxide.V Various other semi-conductive materials for low tension spark plugs are well known in the art. lf desired, an insulator ring may be used in place of .a semi-conductor ring but not to the same advantage since with a semi-conductor high energy low voltage operation can be used to produce an especially hot spark.

Between head portion 40 and projection 42, the centerwire is formed with an annular shoulder 46 having a diameter intermediate those of the head and projection portions. A nickel or other heat and corrosion resistant metal washer 48 having a diameter about the same as that of shoulder 46 -is brazed to the shoulder and is pressed tightly between the shoulder and semi-conductor ringV 44 as shown. Another washer 50 o-f the same or similar material but of larger size is brazed to the inner surface of ange 16, thereby forming part of the ground electrode, and is pressed tightly between the iiange and the' base surfaces of insulator 1S and semi-conductor ring S4. Shoulder 46 Vserves the important function of increasing the distance from the centerwire to the shell by the route between ring 44 and insulator l, and thus insures against internal hash-over which might otherwise occur. The heat and corrosion resistant washers 4S and 5@ function to prevent the formation of an oxide lm between'the semi-conductor ring 44 and the metal surfaces the ring would otherwise Contact. rfhus, intimate electrical contact between the semi-conductor ring and each ofthe electrodes is assured throughout the life of the plug.

Annular'il'ange 16 has an inner surface the upper portion oiwhich, adjacent ring 44, is of cylindrical shape as shown at 52 and the lower end of which tapers outwardly as shown. Cylindrical surface 52 isof the same diameter and is aligned with the inner surface of washer 5G and ring 44. Thus, the combination of these surfaces forms a cy inder or barrel fromwhich the elec trical discharge projects when the igniter is actuated.

To provide adequate cooling, the inner wall of thickerred portion 14 of the shell-is formed with a series of A Y portions and pad l12- are joined together as by the braze and mechanical joints 8 and 11, respectively, and gasket 50 brazed to the inner surface of the ground electrode flange 16. Center electrode 30, with the gasket 48 brazed to shoulder 46, is then inserted into insulator 18 along with the semi-conductor ring 44, and this entire -assembly .--assases Y,

' ground electrode at` one end thereof, an elongated ceramic is then Vpositioned, in the shell, as shown,-and nut. l

threaded tightly into place. By threading the nut 20 Vtightly into the shell, pressure is exerted by insulator 18 Vagainst the upper tapered surface of the head portionV 40 of the centerwire and also against gasket 50 thereby creating a -good electrical contact. As a separate opera- VVtion, Kovar sleeve 34 is positioned with itsV lower portion is counterbore 38 of the upper insulator, the glass and the insulator, and theV assembly is then heated to canse the glass to fuse and to form arbond Vbetween the sleeve and the insulator. After the heating Yoperation the boreV in the thick upper portion of the sleeve is rea-med to remove -any oxide film which is formed. Then this upper insulator-Kovar sleeve assembly is inserted into the shell such that centerwire passes through the Kovar sleeve, Yas shown, after which the upper'portion of the shell is threadedly engaged with the lower portions, as shown at 10, and the flange, at the upper end of the threaded joint 10, turned inwardly and shrink welded- (Cico welded). The centerwire is then brazed to the Kovar sleeve by placing a ring of brazing material around the centerwire, on the top of sleeve 34, and heatingto fuse the brazing material and thereby bond the parts together to thereby complete the assembly.

It is Vdesirable that the centerwire 30 and the metal shell be made of the samemetal, or at least of metals having substantially the same coeicients of expansion. By' this means, pressure is Imaintained on head portion 40 of the electrode, and in turn on semi-conductor ring 44, throughout the operating temperature range of the igniter, the longitudinal expansion of the shell and of the centerwire being virtually the same because of their similar coeicients of expansion. contact between ring 44 and electrodes 16 and 30, respectively, throughout the operating temperature range. A

preferred metal for the centerwire andY for the shell is Y Vthe end thereof adjacent said ground electrode, a ring Qin said recess abutting said ground electrode, the bore of 7^said ring being aligned with the boreV of said ground electrode, and a center electrode in said recess extending partially through said ring into spaced relationship with said ground electrodersaid ring 'bei-ng of a material which electrically insulates said center Yelectrode from said ground electrode. l

2. An igniter plug comprising a generally tubular shaped metal shell having an inwardly extendingannular This assures good electrical Vmixture in powdered form is poured between the sleeve 1 insulator Ysecured within said shell having a bore extending therethrough with an enlarged portion yforming a cylindrical recess at the end thereof adjacent said ground electrode, a center electrode in said insulator bore having a cylindrical head portion positioned in said recess, a ring in said recess pressed between said head portion and said ground electrode, the bore of said ring being aligned with the bore of Ysaid ground electrode, and a cylindrical extension on said head portion extending only partially through said ring into spaced relationship with said ground electrode, said ring being of a material which electrically insulatesssaid center electrode from said ground electrode. v

3. A spark plug as set forthrin claim 2 and wherein the shell and center electrode are of the same metal.

4. An igniter plug comprising a generally tubular shaped metal shell having an inwardly extending annular ground electrode at one end thereof, an elongated ceramic insulator secured Within said shell having a bore extending therethrough with an enlarged portion forming a cylindrical recess at the end thereof adjacent Vsaid ground electrode, a center electrode in said insulator bore having a cylindrical head portion positioned in said recess, an annular shoulder formedon said head portion having a diameter smaller than said head portion, a semiconductor ring in said recess pressed between said shoulder and said ground electrode, the bore of said ring being of Vsubstantially the same diameter and aligned with the boreof saidground electrode, and a cylindrical extension on said head portion extending only partially through said ring into spaced relationship with said ground electrode.

5. A-nv igniter plug ycomprising a generally tubular shaped metal shell having an inwardly. extendingl annular ground electrode at one end thereof, an elongated ceramic insulator secured within said shell having a bore extending therethrough with .an enlarged portion forming a cylindrical recessV at the end thereof adjacent said ground electrode, a center electrode in said Yinsulator bore having a cylindrical head portion positioned in said recess, an annular shoulder formed on said head portion having a diameter smaller than said head portion, a ringV in s'aid recess pressed between said shoulder and said ground electrode, the bore of said ring being of-substantially the same diameter and aligned with the bore of said ground electrode, and a cylindrical extension on said head portion extending only partially through said ring into spaced relationship with said ground electrode, said ring being of a material which electrically insulates said Vcenter electrode from said ground electrode.V

6. An igniter plug comprising Y a generally tubular shaped metal shell having an inwardly extending annular ground electrode at one end thereof, a 'nickel gasket brazed to the inner surface of said yground electrode, an elongated ceramic insulator secured. within said shell having a bore extending therethrough with Van enlarged Y portion forming a cylindrical recess at the end thereof adjacent said ground electrode, a center electrode in said insulator bore having a cylindrical head portion positioned in said recess, an annular shoulder formed on said head portion having a diameter smaller than said head portion, a nickel gasket brazed to said shoulder, a

o into spaced relationship with said ground electrode.'

7. An igniterplug comprisingA a generally tubular shaped metal shell, a ceramic insulator secured within said shell having a bore extending therethrough, a center electrode extending through said insulator bore, a thinwalled metal tube having a diameter greater than that of said center electrode positioned concentrically around and having an upper end bonded to said center electrode, and a glass seal between and bonded to said tube and said insulator, said glass seal and said tube having approximately the same coeftlcients of expansion.

8. An igniter plug comprising a generally tubular shaped metal shell, a ceramic insulator secured within said shell having a bore extending therethrough, an upper portion of Said bore being of large diameter, a middle portion of said bore being of intermediate diameter and a lower portion of said bore being of small diameter, a center electrode extending through said insulator bore, a thin-walled metal tube having a diameter greater than that oi said center electrode positioned concentrically around and having an upper end bonded to said center electrode, the lower end of said tube being of about the same diameter and positioned in the middle portion of said bore, and a glass seal in the upper portion of said bore bonded to said tube and said insulator, said glass seal and said tube having approximately the same coefficients of expansion.

9. An igniter plug comprising a generally tubular shaped metal shell having an inwardly extending annular ground electrode at one end thereof, aligned upper and lower' elongated ceramic insulators secured within said shell each having a bore extending therethrough, the bore of lower insulator having an enlarged portion forming a cylindrical recess at the end thereof adjacent said ground electrode, a center electrode extending through said insulator bores having a cylindrical head portion positioned in said recess, a ring in said recess between said head portion and said ground electrode, the bore of said ring being of substantially the same diameter and aligned with the bore 'of said ground electrode, a cylindrical extension on said head portion extending only partially through said ring into spaced relationship with said ground electrode, said ring `being of a material which electrically insulates said center electrode from said ground electrode, a thin-Walled metal tube having a diameter greater than that of said center electrode positioned concentrically around and having an upper end brazed to the portion of said center electrode within said upper insulator, and a glass seal between and bonded to said tube and said upper insulator, said glass seal and said tube having approximately the same coecients of expansion.

10. An igniter plug comprising a generally tubular shaped metal shell having an inwardly extending annular ground electrode at one end thereof, an elongated ceramic insulator secured Within said shell having a centerbore therethrough, a ring of semi-conductor material positioned at the end of said insulator and abutting said ground electrode, the bore of said ring being aligned with the centerbore of said insulator and with the bore of said ground electrode, and a center electrode in said insulator centerbore extending partially through said ring into spaced relationship with said ground electrode.

References Cited in the tile of this patent UNITED STATES PATENTS 

